Issues with Dart preference page

[vogella]

If the user inputs an incorrect Dart location, the Apply button becomes inactive, it remains inactive, even if the user changes something.

Restore Defaults simply remove the user input, please use something more reasonable, like a check which checks the typical install locations and uses the one that could be confirmed.

It would IMHO also beneficial, if you could add a "Validate" button, so that the user can see if the location is valid.